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Friday 19 January 2018

Pregnant ewes must be managed correctly to ensure the best results

Sheep

Dr Tommy Boland

We SLAUGHTERED 38 lambs last Monday, with an average live weight of 48kg. These lambs produced an average carcass weight of just over 23kg, with the factory paying up to 23kg. This represents a kill out above 48pc, which is excellent for this time of year. Over the past two weeks, the remainder of the lambs have averaged 42kg with a growth rate of 190g/day.

Grass growth on the farm was 35kg DM/ha/day up to last week. The very heavy rain at the beginning of last week made grazing conditions more difficult, but the land demonstrated a great ability to soak it and at the time of writing is recovering well.

All our ewes and indeed ewe lambs were mated using laproscopic AI in mid October, to a synchronised oestrus. Rams will go out this morning to pick up repeats. Hopefully we will avoid the situation we had last year where a number of ewes did not demonstrate heat during the two repeat cycles, and ultimately ended up barren. This has been linked to a phenomenon called deep anoestrous, whereby the ewes don't show heat until the rams have been removed.

Our sheep technician, Pat Quinn, scored the ewes on their body condition one week prior to mating, and the flock average was 3.25, right in the middle of the target range of 3-3.5. We're really pleased with this as it should lay a good foundation for the rest of pregnancy. As the old saying goes, 'Tús maith leath na hoibre', or 'A good start is half the work'. The other half, however, is equally as important.

We all focus on flushing the ewe and steaming up but the intervening time is also important. The number of lambs a ewe actually produces is always less than her potential (or the number of eggs ovulated), but we can influence this somewhat by correct management.

The first four-to-six weeks after mating are crucial in terms of embryo mortality, and incorrect feeding or stress can have a significant impact. Incorrect feeding includes both feeding ewes too much, as well as too little. With excessive over feeding in the first few weeks, blood progesterone levels can be lowered, and as this is the hormone responsible for the maintenance of pregnancy, embryonic mortality can be increased.

For the first two weeks after fertilisation, the embryo is "free floating" in the womb. During this time it is critical that all forms of stress are avoided until such time as the embryo becomes firmly attached to the uterus. This attachment takes place from the third week onwards.

The second and third months of pregnancy are often over-looked. This equates to the period between mid-November and mid-January for a mid-March lambing flock. While correct management at this stage won't guarantee a successful lambing outcome, inadequate management can have negative effects.

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It is during this time that the size of the placenta is determined and this, in turn, affects the number of attachments the lamb has to its mother and the lamb's ultimate size at birth. Remember an extra 1kg at birth means about 2.5kg at weaning.

The size of the placenta is determined by the end of the third month of pregnancy. In order to produce good-sized lambs at birth, the first requirement is that the ewe should produce a large placenta.

There are specific points on the uterine wall (caruncles) where the placenta attaches itself and through which nutrients fed to the ewe make their way to nourish the unborn lamb.

A single foetus can take advantage of all of these caruncles, whereas multiple foetuses must share them. This fact is largely responsible for twin lambs being smaller than singles.

In order to get ewes to produce large placentas, they should be fed so they lose weight (5-7pc) in the middle two months of pregnancy, if they are in good, fit condition after mating. However, this principle shouldn't be applied to thin ewes, where it has been shown that weight loss in mid pregnancy can result in a lower placenta size and reduced lamb birth weight.

When ewes are in good condition in mid pregnancy, overfeeding will reduce their intake capacity in late pregnancy, which can impact negatively on a lamb's birth weight.

Dr Tommy Boland is a UCD lecturer in sheep production. Email: tommy.boland@ucd.ie

Indo Farming